Many types of equipment require some means of temperature control, either by heating or cooling, in order to function effectively. In general, such equipment consists of three elements: The component requiring temperature control, a heat transfer device, and a medium acting as a thermal energy sink or source. Some equipment, such as those that transfer heat from one medium to another, require heat transfer devices for supplying and removing heat.
In general, equipment which require small amounts of, or low watt-density, cooling, use natural or forced convection air cooling. On the other hand, equipment which requires large amounts of, or high watt-density, cooling, or precise temperature control, or operating temperatures at or below ambient air temperature use something other than air for cooling. Such techniques incorporate liquid cooling, thermoelectric cooling, or Freon compressor/condenser cooling.
In the home refrigerator, for example, heat is transferred from the inside of the refrigerator cabinet to the air outside. The refrigeration unit has two heat transfer devices. Inside the refrigerator there is typically an extruded air heat sink and fan which provides forced air convection to remove heat from the source medium, the air inside the refrigerator, and to transfer the heat to the refrigeration unit. Outside the refrigerator, heat from the refrigeration unit is transferred by an external radiator via natural convection into the heat sink medium, i.e., the surrounding air. However, for other applications that require a more efficient thermal energy transport system, liquids can readily provide the medium by which heat is transferred.
The transfer of heat by a liquid medium is often accomplished with a heat transfer plate, sometimes called a xe2x80x9ccold platexe2x80x9d. A cold plate is typically a flat metal plate in contact with a flowing fluid. Thermally conductive metals, such as aluminum or copper, are commonly used for the plate, although other metals, such as stainless steel, may be used in corrosive environments. Components requiring temperature control are mounted onto an exterior surface of the cold plate.
The thermal efficiency of the cold plate depends upon the amount of surface area of the cold plate in contact with the flowing fluid, the degree of turbulence of the flowing fluid, and the efficiency of thermal contact between the components and the cold plate. It is desirable for a liquid cold plate to have a high degree of thermal efficiency, while at the same time be simple and inexpensive to manufacture. Simple and low-cost manufacturing is commonly achieved with a cold plate formed by a flat aluminum plate with copper tubing glued or pressed into grooves in the surface of the aluminum plate. Such designs have very low surface areas in contact with the flowing fluid, which provide limited heat transfer and have very high pressure drops to limit the amount of coolant that can be used. On the other hand, high efficiency heat transfer is commonly achieved with cold plates that have a large amount of surface area in contact with the cooling fluid. Such cold plates are typically either not flat and complex (e.g., shell and tube designs), or very expensive to manufacture (e.g., brazed plate-fin designs).
One example of cold plate use is the environment friendly, hybrid diesel/electric vehicles. Such vehicles have both diesel engines and electric motors for propulsion and use only half the fuel of standard diesel vehicles. The electronic components used to drive the electric motor generate considerable heat in a small area (approximately 100 watts/sq.in.) that must be transferred to the coolant system and ultimately transferred to the ambient air via the radiator. High-efficiency, low pressure drop, liquid cold plates must be used to transfer this heat into the coolant. Presently, only brazed plate-fin heat exchangers meet both these requirements. Unfortunately, brazed plate-fin heat exchangers are very expensive and thus drive up the costs of the vehicles, which slow their introduction into the marketplace.
Thus the desire for cold plates which are simple and easy-to-manufacture at low costs conflicts with the desire for cold plates with high heat transfer efficiency. However, the present invention resolves these conflicting desires with a cold plate that has high heat transfer, but which is also simple and inexpensive to manufacture. The present invention provides the same attributes of brazed plate-fin cold plates, high rates of heat transfer and low pressure drop, at only a fraction of the costs.
The present invention provides for a liquid heat transfer plate formed from a unitary, one-piece, plate which has a first flat surface and an opposite second flat surface and a plurality of fluid channels between said first and second surfaces. Each of the fluid channels has a cross-section with a major axis perpendicular to the first and second surfaces, and a minor axis perpendicular to and shorter than the major axis. The plate also has first and second ends perpendicular to the fluid channel direction and a first manifold near the first plate end. The manifold is perpendicular to the fluid channel and is fluidly connected to the fluid channel. The plate also has a second manifold near the second plate end perpendicular to the fluid channel and fluidly connected to the fluid channel. First and second caps fixed to the first and second plate ends respectively seal the fluid channel in the plate.
The present invention also provides for a process of manufacturing a heat transfer plate. A preform having first surface and a second surface opposite the first surface and a plurality of fluid channels in a first direction between the first and second surfaces is first extruded. Each of the fluid channels has a cross-section perpendicular to the first direction, with the cross-section having a major axis perpendicular to the first and second surfaces, and a minor axis perpendicular to and shorter than the major axis. Then the preform is cut in a second direction perpendicular to the first direction to define a plate having first and second ends. A first manifold is drilled near the first plate end perpendicular to the fluid channel so that the fluid channel is fluidly connected to the first manifold. A second manifold is drilled near the second plate end perpendicular to the fluid channel so that the fluid channel is fluidly connected to the second manifold. First and second caps are fixed to the first and second plate ends respectively to seal the fluid channel in the plate, and at least one of the first and second surfaces of the plate is leveled.
The resulting heat transfer plate is inexpensive to manufacture, flexible in design, and has high heat transfer performance capabilities.